Double beam fluorometer using an alternately activated double beam lamp



i 3, 1966 MY. LAIKIN ETAL 3,249,754 7 DOUBLE BEAM FLUOROMETER USING AN ALTERNATELY ACTIVATED DOUBLE BEAM LAMP Filed March 26, 1962 FIG. 1 M. I. Q 29 VOLTAGE SUPPLY v 27 D/SCR/M/NATOR I NVENTOR5 MILTON LA/K/N,

DA W0 A. RoHRER BY THE/R ATTORNEYS HARE/5, K/EcH, Russ/51.4 Jc/(sxezv United States Patent DOUBLE BEAM FLUOROMETER USING AN AL- This invention relatesto lamps and radiation measurement and, in particular, to double beam lamps and double beam measuring equipment.

Lamps are desired which produce two beams of radiation for energizing sample and reference paths in measuring equipment, such as fiuorometers and spectrophotometers. Parameters may changeduring the operation of such equipment and it is desired to provide systems which maintain known or controlled ratios of radiation intensity in the paths. Accordingly, it is an object of the present invention to provide a new and improved double beam lamp which provides a constant intensity ratio of the two sources in the lamp. A further object is to provide such a lamp having a single cathode and a pair of anodes, with the lamp producing equal electron currents in the two anodes.

It is an object of the invention to provide a double beam lamp in which the two light sources are energized alternately and in which a dark period between energization of the sources is obtained. A particular object is to provide such a lamp which is operable in the ultraviolet region and one which may be utilized to provide a concentrated radiation in a narrow band or a continuum, as desired.

It is an object of the invention to provide a double beam lamp having the desirable operating characteristics described herein whilehaving relatively low power requirements and producing relatively small amounts of heat. A further object is to provide such a lamp which may utilize conventional electron tube mounting arrangements. Another object is to provide such a lamp which may conveniently be inserted into and removed from a socket positioned in a casting or other suitable housing. It is a particular object of the invention to provide a new and improved envelope shape including an annular groove adjacent the upper end of the tube for extraction from the socket.

It is an object. of the invention to provide a double beam lamp for a fluorometer or the like including an envelope containing an ionizable gas, a thermionic cathode mounted within the envelope, means for heating the cathode to produce electron emission therefrom, first and second anodes mounted within the envelope and spaced from the cathode, a shield mounted within the envelope between the anodes and defining first and second anode zones within the envelope, and means for applying a positive potential alternately between the first and second anodes and the cathode to generate electron beams alternately through the first and second zones for producing light sources alternately in the zones. A further object is to provide such a structure in which the anodes and shield are of particular shape to concentrate the ionized gas adjacent the envelope surface. Another object is to provide such a structure in which the inner wall of the envelope is coated with phosphor for excitation by ionized gas to produce a broad band radiation.

The invention also comprises novel details of construction and novel combinations and arrangements of parts, which will more fully appear in the course of the following description. The drawing merely shows and the description merely describes the preferred embodiment of Patented May 3, 1966 the present invention which is given by way of illustration or example.

In the drawing:

FIG. 1 is a plan view of a fluorometer, shown partly in section and partly diagrammatic, illustrating a preferred embodiment of the invention;

FIG. 2 is a side view of the lamp of the embodiment of FIG. 1;

FIG. 3 is an enlarged sectional view of the lamp of FIG. 2;

FIG. 4 is an enlarged perspective view of the lamp With the envelope removed;

FIG. 5 is an enlarged view of a portion of the lamp of FIG. 4 showing some cathode support detail; and

FIG. 6 is a schematic diagram illustrating the operation of the lamp.

The fluorometer of FIG. 1 includes a housing casting 20, a double beam lamp 21, a reference material container 22, a sample carrier 23 with a plurality of sample material containers 24, a radiation detector 25, an amplifier 26, a discriminator 27, an output indicating meter 28, and a voltage supply 29 for the detector 25.

The housing provides a beam path from the lamp 2] through a filter 32 to the reference material container on the knob 39' of the shaft 39 to move the carrier 23 to the left. Then rotation of the knob or pushing on the knob may rotate the carrier to position another sample container in the radiation path when the carrier is again moved to the right to the position shown in FIG. 1.

The lamp 21 alternately produces a beam of radiation along the path to the reference container 22 and along the path to the sample container 36. The structure and operation of the lamp will be described in greater detail hereinbelow. The output of the detector 25 will have two components, the one varying as a function of the fluorescence of the reference material and the other varying as a function of the fluorescence of the sample material. The radiation detector output is amplified in the amplifier 26 and connected as an input to the discriminator 27. An A.C. signal which is synchronous with the flashing of the lamp 21 is connected to terminals 40 of the discriminator to separate sample and reference signals. The discriminator'may be a conventional circuit producing a first output on line 4-1 varying. as a function of the fluorescence of the sample material and a second output on the'line 42 varying as a function of the fluorescence of the reference material. The output 41 is coupled to the output indicating meter 28 for visual observation and/or recording. The output 42 is connected in controlling relation-to the voltage supply 29 for varying the magnitude of the dynode voltage supply to the radiation detector 25 to maintain the output 42 substantially constant. The output of the detector is a function of its supply voltage as well as a function of the fluorescence of the reference and sample materials and the intensity of the radiation from the lamp. The feedback circuit in the reference half of the system provides means for maintaining system operation at a constant level independent of variations in supply voltages, lamp output and detector sensitivity.

Such a reference feedback system will work with any detector the gain of which varies with supply voltage, e.g., a photomultiplier such as R.C.A. 931A. A detector having a gain which does not vary With supply voltage, e.g., a photo diode such as R.C.A. 935, may also be used connection therebetween.

be an elongate wire coil positioned within the cathode and 3 with the double beam lamp but a different means is required to determine the ratio of sample to reference. This may take the form of a commercially available ratio indicating meter.

The lamp 21 is formed in a glass envelope 45 with a conventional nine-pin base 46. The electrode structure is carried within the envelope on the pins following conventional tube construction techniques. The envelope is evacuated, charged with a quantity of mercury vapor or other suitable ionizable gas, and sealed at the tip 47. The glass envelope is preferably formed with an annular groove 48 adjacent the tip end to provide a tripping zone for removing the lamp from the instrument housing. A U- shaped clamp 49 having inwardly turned shoulders 50 at each end for engaging the groove 48 of the lamp is shown in FIG. 2. The lamp is easily inserted into the conventional nine-pin socket by applying pressure on the tip end. The lamp may be removed by positioning the shoulders 50 of the clamp in the groove 48 of the lamp, compressing the sides of the clamp toward each other, and applying a pulling force thereto.

The lamp includes a resistance wire heater 53, a thermionic cathode 54, anodes 55, 56 and a' shield 57. The cathode, anodes and shield are positioned between mica spacer plates 58, 59. The anodes and shield are provided with tabs at the upper and lower edges, which tabs project through openings in the spacer plates and are twisted to fix the anodes and shield in place. The lower tabs are spot welded to appropriate pins of the base 46 for supporting the electrode structure within the envelope. The cathode 54 is a tubular or box-like structure which extends through the spacer plates and has a peripheral shoulder 60 for supporting the cathode on the lower spacer plate 59 (FIG. A tab 63 may be connected between the upper end of the cathode and the shield to provide an electrical The resistance heater 53 may connected to two pins of the base;

The cathode 54 preferably is centrally positioned within the envelope and is equally spaced from the anodes 55, 56. The shield 57 is positioned between the two anodes to provide visual and electrical isolation therebetween. The anodes are preferably positioned adjacent the wall of the envelope in order to concentrate the glow of the lamp adjacent the envelope wall.

A preferred form for the electrode structure is shown in FIGS. 3 and 4. The shield 57 encloses the cathode 54 except for relatively large central apertures 64, 65 facing the anodes 55, 56, respectively. The shield extends substantially to the wall of the envelope, preferably with diverging wings 66 to provide maximum isolation between the anodes.

The anode 55 is preferably a channel-shaped structure with wings or fins 67 directed toward the envelope wall and a large central aperture 68. The anode 56 is similarly shaped. The shield may be provided with fins 69 which project outward toward the anodes substantially parallel to the fins 67. The fins 69 serve to collect positive ions and to concentrate the discharge in the region of the anode 55 rather than toward the wings 66. Collection of positive ions reduces the number of such ions that may collide with the emission coating on the cathode 54.

In operation, electrons in the electron stream from the cathode to an anode collide with mercury atoms exciting the atoms and ionizing the excited atoms to generate radiation. This radiation is concentrated in the zone enclosed by an anode adjacent the envelope wall. The inner wall of the envelope preferably carries a coating 72 of phosphor which is excited by the ultraviolet radiation of the mercury vapor, fluorescing and generating radiation of a longer wavelength. By suitably choosing the phosphor coating material, a continuum can be obtained for the spectral region desired. This type of lamp output is highly desirable for many measurements, particularly in the measurement of fluorescent characteristics where the sample is responsive to relatively narrow bands of radiation. When the lamp or other radiation source provides output only in a few rather narrow lines or bands, quite often this radiation does not coincide with the sensitive bands of the sample and significant characteristics of the sample are missed. In contrast, radiation having a continuum assures analysis of the sample over a Wide spectral range.

A circuit suitable for energizing the lamp for use in the instrument of FIG. 1 is shown in FIG. 6. An A.C. source is connected to primary win-ding 80 of the transformer 81. This A.C. source would normally be the same source which is connected to the terminals of the discriminator. The center tap of the secondary winding 32 is connected to the shield 57. One end of the secondary is connected to the anode 56 through a current limiting resistor 83 and the other end is connected to the anode through a similar resistor 84. The resjstance heater 53 may be energized from another winding 85 on the transformer and preferably has one end of the winding 85 connected to the center tap of the winding 82.

The lamp is intended for operation in the range of 40 to 1,000 cycles per second. The resistance heater is continuously energized and provides a source of heat for the thermionic cathode. A positive potential rela tive to the cathode is alternately applied to each of the anodes resulting in an electron beam alternately in each half of the envelope producing alternate beams of radiation from each half of the lamp. The lamp does not fire immediately upon reversal of polarity of the source,

. requiring a potential buildup on the anode with respect to the cathode. This delay provides the desired dark period between firings of the two sections of the lamp. The lamp discharge is extinguished on polarity reversal. When a phosphor coating is used, a low persistence phosphor preferably is selected. The common cathode operated from the center tap of the winding which provides the potential for each of the anodes produces an equal electron current in the two sections of the lamp resulting in the desired constant ratio of intensity of the two radiation sources. With this desirable characteristic, the lamp may be operated from a power source of varying amplitude without adversely affecting the accuracy of the measuring system.

The lamp is preferably operated with a low pressure mercury vapor atmosphere, typically in the range of six to ten microns mercury vapor pressure. A major portion of the energy in the radiation due to ionization of mercury atoms will lie in the 253.7 millimicron resonance line. For certain applications where energy of this wavelength is desired, the lamp may be operated with no phosphor coating.

Normally a lamp with a broad excitation band is desired and this may be obtained by providing a phosphor coating in the lamp. Typically, the phosphor will be a material which has a peak emission at 355 millimicrons, such as cerium activated calcium phosphate or lead activated barium silicate. A material of this type when excited by radiation from ionized mercury vapor provides a continuum over the range of 313-407 millimicrons. For certain purposes, another type of phosphor having a peak emission at about 315 millimicrons, such as calcium thallium phosphate may be used. This type of material provides a continuum over the range of 260- 350 millimicrons. Such phosphors are commercially available and are applied in the conventional manner.

Conventional electron tube materials may be used in the electrode structure. In one preferred embodiment, the heater is a ceramic coated tungsten wire and the cathode an oxide coated nickel alloy. The anodes and shield are nickel.

A double beam lamp for use in a fiuorometer or the like should be relatively small and with relatively low heat output as it is desirable to position the lamp quite close to the sample and reference materials to obtain I maximum efiiciency and a compact design. The particular lamp. described above is less than two inches tall and operates with less than six watts total power. This permits the lamp to be positioned less than an inch and one-half from the sample and reference materials without causing adverse heating effects on the materials.

Although an exemplary embodiment of the invention has been disclosed and discussed, it will be understood that other applications of the invention are possible and' that the embodiment disclosed may be subjected to various changes, modifications and substitutions without necessarily departing from the spirit of the invention.

We claim as our invention: 1. In a double beam lamp for a fiuorometer or the like, the combination of:

an envelope containing an ionizable gas; a thermionic cathode mounted within said envelope; means for heating said cathode to produce electron emission therefrom; first and sec-ond anodes mounted within said envelope and spaced from said cathode, said anodes having apertures therein-for the transmission of radiant energy through said anodes; an opaque shield mounted within said envelope between said anodes, said shield defining first and second optically isolated anode zones within said envelope; and means for applying a positive potential alternately between said first and second anodes and said cathode to generate electron beams alternately through said first and second zones for producing light sources alternately in said zones. 2. In a double beam lamp for a fluorometer or the like, the combination of:

an envelope containing a gas which produces radiation when ionized; a thermionic cathode mounted within said envelope; means for heatingsaid cathode to produce electron emission therefrom; v first and second anodes mounted within said envelope adjacent the wall thereof and substantially equally spaced from said cathode, said anodes having at least one aperture therein for the transmission of radiant energy through said anodes; an opaque shield mounted within said envelope and extending substantially to the surface thereof between said anodes, said shield defining first :and second optically isolated anode zones within said envelope;

and means for applying a positive potential alternately between said first and second anodes and said cathode to generate electron beams alternately through said first and second zones.

3. In a double beam lamp for a fiuorometer or the like.

the combination of:

an envelope containing a gas which produces radiation when ionized; V

a thermionic cathode centrally mounted within said envelope;

.means for heating said cathode to produce electron emission therefrom;

first and second anodes mounted within said envelope adjacent the wall thereof on opposite sides of and substantially equally spaced from said cathode, said anodes having at least one aperture therein for the transmission of radiant energy through said anodes;

an opaque shield mounted within said envelope and extending substantially to the surface thereof between said anodes, 'said shield defining first and second optically isolated anode zones within said envelope, said shield including a portion disposed about said cathode with said portion having apertures facing said zones providing unimpeded beam paths from said cathode into each of said zones;

and means for applying a positive potential alternately between said first and second anodes and said cathode to generate electron beams alternately through said first and second zones.

4. In a double beam lamp for a fluorometer or the like,

the combination of:

a tubular envelope containing a gas which produces radiation when ionized;

an elongated thermionic cathode mounted within said envelope along the axis thereof;

means for heating said cathode to produce electron emission therefrom;

first and second anodes mounted within said envelope adjacent the wall thereof on opposite sides of and substantially equally spaced from said cathode, each of said anodes having a large central aperture and edge fins projecting toward said envelope;

a shield mounted within said envelope and extending substantially to the surface thereof between said anodes, said shield including fins disposed substantially parallel to the fins of the respective anodes defining first and second anode zones within said envelope, said shield including a portion disposed about said cathode having apertures aligned with the apertures of the respective anodes;

and means for applying a positive potential alternately between said first and second anodes and said cathode to generate electron beams alternately through said first and second zones.

5. In a double beam lamp for a fluorometer or the like,

the combination of:

an envelope containing a quantity of mercury vapor;

a thermionic cathode mounted within said envelope;

means for heating said cathode to produce electron emission therefrom; I

first and second anodes mounted within said envelope adjacent the wall thereof and substantially equally spaced from said cathode, each of said anodes having a large central aperture therein;

an opaque shield mounted within said envelope and extending substantially to the surface thereof between said anodes, said shield defining first and second optically isolated anode zones within said envelope;

and means for applying a positive potential alternately between said first and second anodes and said cathode to generate electron beams alternately through said first and second zones producing ionization of mercury vapor in said zones as sources of radiation.

6. In a double beam lamp having a continuum, the

- combination of:

an envelope containing a quantity of mercury vapor and having a coating of phosphor on the inner surface;

a thermionic cathode mounted within said envelope;

means for heating said cathode to produce electron emission therefrom;

first and second anodes :mounted within said envelope adjacent said coating and substantially equally spaced from said cathode, each of said anodes having a large central aperture therein;

an opaque shield mounted within said envelope and extending substantially to the surface thereof between said anodes, said shield defining first and second optically isolated anode zones within said envelope;

and means for applying a positive potential alternately between said first and second anodes and said cathode to generate electron beams alternately through said first and second zones producing ionization of mercury vapor in said zones with resultant excitation of adjacent phosphor areas to provide two light sources.

'7. In a double beam fluorometer, the combination of:

a lamp including an envelope containing a gas which produces radiation when ionized, a thermionic cathode for producing electron emission, first and second anodes adjacent the envelope wall and substantially equally spaced from said cathode, and a shield extending substantially to the envelope wall between said anodes and defining first and second anode zones;

a radiation detector;

means defining first and second beam paths from the first and second anode zones respectively to said detector;

means for positioning a reference material in said first path;

means for positioning a sample material in said second path; a

means for coupling an A.C. potential to said anodes and said cathode to alternately ionize the gas in said first and second zones providing first and second radiation sources;

discriminator means having said detector coupled as an input thereto and having means for connecting the A.C. potential thereto for producing a first output varying as a function of the fluorescence of said reference material and a second output varying as a function of the fluorescence of said sample material;

and feedback means for varying the supply voltage to said detector as a function of said first output to maintain said first output constant.

. In a double beam fluorometer, the combination of:

a lamp including an envelope having a coating of phosphor on the inner surface and containing a quantity of mercury vapor, a thermionic cathode for producing electron emission, first and second anodes adjacent the envelope wall and substantially equally spaced from said cathode, and a shield extending substantially to the envelope wall between said anodes and defining first and second anode zones;

a radiation detector;

means defining first and second beam paths from the first and second anode zones respectively to said detector;

means for positioning a reference material in said first path;

means for positioning a sample material in said second path;

means for coupling an A.C. potential to said anodes and said cathode to alternately ionize the mercury vapor and excite the phosphor area in said first and second zones providing first and second sources of continuum radiation;

discriminator means having said detector coupled as an input thereto and having means for connecting the A.C. potential thereto for' producing a first output varying as a function of the fluorescence of said reference material and a second output varying as a function of the fluorescence of said sample material;

8 and feedback means for varying the supply voltage to said detector as a function of said first output to maintain said first output constant. 9. In an alternating double beam lamp for a fluorometer or the like, the combination of:

an envelope containing a gas which produces radiation when ionized;

a tubular thermionic cathode mounted within said envelope;

a resistance heater positioned within said cathode;

first and second anodes mounted within said envelope adjacent the wall thereof and substantially equally spaced from said cathode, each of said anodes having a large central aperture therein;

a shield mounted within said envelope and extending substantially to the surface thereof between said anodes, said shield defining first and second anode zones within said envelope;

a transformer having a primary winding and a center tapped secondary winding with the tap connected to said shield and cathode and with the secondary winding ends connected to said anodes respectively;

means for connecting said heater to a power source to heat said cathode for electron emission;

and means for connecting an A.C. source to said primary winding for applying a positive potential alternately between said first and second anodes and said cathode to generate electron beams alternately through said first andsecond zones and ionize the gas therein.

References Cited by the Examiner RALPH G. NI'LSON, Primary Examiner.

GEORGE N. WEST-BY, Examiner.

C. R. CAMPBELL, W. F. LINDQUIST,

Assistant Examiners. 

1. IN A DOUBLE BEAM LAMP FOR A FLUOROMETER OR THE LIKE, THE COMBINATION OF : AN ENVELOPE CONTAINING AN IONIZABLE AS; A THERMIONIC CATHODE MOUNTED WITHIN SAID ENVELOPE; MEANS FOR HEATING SAID CATHODE TO PRODUCE ELECTRON EMISSION THEREFROM; FIRST AND SECOND ANODES MOUNTED WITHIN SAID ENVELOPE AND SPACED FROM SAID CATHODE, SAID ANODES HAVING APERTURES THEREIN FOR THE TRANSMISSION OF RADIANT ENERGY THROUGH SAID ANODES; AN OPAQUE SHIELD MOUNTED WITHIN SAID ENVELOPE BETWEEN SAID ANODES, SAID SHIELD DEFINING FIRST AND SECOND OPTICALLY ISOLATED ANODE ZONES WITHIN SAID ENVELOPE; AND MEANS FOR APPLYING A POSITIVE POTENTIAL ALTERNATELY BETWEEN SAID FIRST AND SECOND ANODES AND SAID CATHODE TO GENERATE ELECTRON BEAMS ALTERNATELY THROUGH SAID FIRST AND SECOND ZONES FOR PRODUCING LIGHT SOURCE ALTERNATELY IN SAID ZONES.
 7. IN A DOUBLE BEAM FLUOROMETER, THE COMBINATION OF: A LAMP INCLUDING AN ENVELOPE CONTAINING A GAS WHICH PRODUCES RADIATION WHEN IONIZED, A THERMIONIC CATHODE FOR PRODUCING ELECTRON EMISSION, FIRST AND SECOND ANODES ADJACENT THE ENVELOPE WALL AND SUBSTANTIALLY EQUALLY SPACED FROM SAID CATHODE, AND A SHIELD EXTENDING SUBSTANTIALLY TO THE ENVELOPE WALL BETWEEN SAID ANODES AND DEFINING FIRST AND SECOND ANODE ZONES; A RADIATION DETECTOR; MEANS DEFINING FIRST AND SECOND BEAM PATHS FROM THE FIRST AND SECOND ANODE ZONES RESPECTIVELY TO SAID DETECTOR; MEANS FOR POSITIONING A REFERENCE MATERIAL IN SAID FIRST PATH; MEANS FOR POSITIONING A SAMPLE MATERIAL IN SAID SECOND PATH; MEANS FOR COUPLING A A.C. POTENTIAL TO SAID ANODES AND SAID CATHODE TO ALTERNATELY IONIZE THE GAS IN SAID FIRST AND SECOND ZONES PROVIDING FIRST AND SECOND RADIATION SOURCES; DISCRIMINATOR MEANS HAVING SAID DETECTOR COUPLED AS AN INPUT THERETO AND HAVING MEANS FOR CONNECTING THE A.C. POTENTIAL THERETO FOR PRODUCING A FIRST OUTPUT VARYING AS A FUNCTION OF THE FLOURSCENCE OF SAID REFERENCE MATERIAL AND A SECOND OUTPUT VARYING AS A FUNCTION OF THE FLOURSCENCE OF SAID SAMPLE MATERIAL; AND FEEDBACK MEANS FOR VARYING THE SUPPLY VOLTAGE TO SAID DETECTOR AS A FUNCTION OF SAID FIRST OUTPUT TO MAINTAIN SAID FIRST OUTPUT CONSTANT. 